In an ultrasonic diagnostic apparatus of recent years, a linear power supply, such as a dropper and a series regulator, with little noise is often used as a power supply of a substrate and the like. However, conversion efficiency of the linear power supply is poor. Heat generation and mounting area of the linear power supply are large, and the cost is high in some cases.
Therefore, a switching power supply with a high conversion efficiency and low cost is used in some cases as a power supply of an ultrasonic diagnostic apparatus of recent years. The switching power supply is a power supply that generates arbitrary different voltages by switching on and off a transistor. The number of times that the transistor is switched per second is called a switching frequency.
However, the switching power supply generates noise every time a switching operation is performed. There is a problem that the generated switching noise is mixed in a signal in an analog circuit or the like of the ultrasonic diagnostic apparatus, and image noise is generated in an ultrasonic image.
Examples of a technique of reducing the image noise include a method of using a shield to cover the switching power supply that is a source of noise and a method of incorporating a low-pass filter using analog elements of RLC into a power output. In addition, an example of a technique of resolving high-frequency noise includes a method of synchronizing a frequency of switching operation with an integral multiple of a transmission timing frequency of a transmission pulse to thereby adjust a noise phase and execute correlation processing to cancel Doppler noise.
An object of the present invention is to provide an ultrasonic diagnostic apparatus that removes image noise caused by a switching operation of switching power supply circuitry.